The need to produce differently colored parts consecutively, wherein each part is homogeneously colored, is increasingly important. For example, in-line vehicle sequencing requirements in the motor vehicle industry mandate that parts be supplied to vehicle manufacturers pre-sequenced in the color required for each consecutive vehicle on the assembly line. As a result, parts suppliers must be able to provide differently colored parts on an as needed basis.
A conventional method of making differently colored parts consecutively, wherein each part is homogeneously colored, employs a single injection molding machine which includes a single resin source, multiple colorant sources, a single injection channel and a single mold. After one or more parts are made with a particular colored resin, the injection channel must be purged of that resin so that a differently colored resin can be introduced into the machine. U.S. Pat. No. 3,674,398, for instance, shows a method and apparatus for purging residual material from a mixing chamber and an injection channel of an injection molding machine. This purging cycle requires additional time to perform and results in loss of molding material.
Another method of consecutively making differently and homogeneously colored parts uses multiple molds, each of which is connected to a dedicated injection channel and a dedicated colored resin source. U.S. Pat. No. 3,178,497, for example, shows a method and an apparatus for making single or multi-color, multi-stage injection molded products that incorporate multiple resin sources and multiple molds. Because of the multiple resin sources and multiple molds, this method and apparatus involve significant capital costs.